The present invention relates to an optical observation apparatus including an ocular optical system, such as binoculars and a monocular.
The optical observation apparatus including an ocular optical system is provided with an eyepiece cup (or eyecup) used for matching a position of an observer's eye to an eye point of the optical observation apparatus. When the observer's eye is naked, the eyepiece cup is protruded with respect to the ocular optical system to be brought into press contact with an observer's face around the eye. When the observer uses eyeglasses, the eyepiece cup is retracted to be brought into press contact with a lens of the eyeglasses.
For example, as an eyepiece cup for binoculars, a protrudable eyepiece cup which is protrudable and retractable to an arbitrary position with respect to the ocular optical system. In particular, a rotating protrudable eyepiece cup using a cam mechanism is easier to stop at an arbitrary position as compared with a straight protrudable eyepiece cup disclosed in Japanese Patent Laid-Open No. 2007-232764.
However, in Japanese Patent Laid-Open No. 2007-232764, an introducing groove portion which introduces a protrusion formed on a lens barrel into a non-penetrated cam groove portion formed on an inner circumferential surface of the eyepiece cup and opens at one side opening portion of the eyepiece cup is formed on the inner circumferential surface of the eyepiece cup. The introducing groove portion facilitates assembly of the eyepiece cup to the lens barrel, but makes drop-off of the eyepiece cup from the lens barrel easy.
Japanese Patent Laid-Open 2007-232764 discloses a configuration in which, in order to prevent the drop-off of the eyepiece cup, the lens barrel is divided into a first lens barrel and a second lens barrel, and the first lens barrel to which the eyepiece cup is attached is screwed to the second lens barrel. Such a constitution makes the drop-off of the eyepiece cup from the lens barrel hard, but increases the number of parts because of the division of the lens barrel into two and increases a diameter of the eyepiece cup since a space for coupling the two lens barrels is needed.
Thus, conventional rotating protrudable eyepiece cups including one disclosed in Japanese Patent Laid-Open 2007-232764 have a complicated configuration which is hard to be miniaturized.